The fate of water from melting ground ice in degrading permafrost environment

在影响加拿大北部可持续发展的冻土退化相关地质灾害中，融解沉降的脆弱性是普遍存在的。冻土的融化固结与含水量、冻土结构、土壤质地、融化速率和孔隙水压力消散密切相关。然而，人们对退化的永久冻土中融化的地面冰的水的命运知之甚少。孔隙水的耗散是如何控制融水固结的？融水流入地下的地方？融化的水是在深处重新补给含水层，还是在地表迁移，最终进入湖泊、河流和海洋？***作为一种研究假设和正反馈，依赖于孔隙水压力消散的融化沉降加速了多年冻土退化的速度。地表暖界向深层退化的多年冻土体下移，加速了多年冻土的融化。为了验证这一研究假设，目标是：***1)在现场观察、描述和监测多年冻土退化的过程；***2)通过实验室试验测量富冰多年冻土的融化固结特性；***3)模拟在退化的多年冻土中发生的传热、融化固结和融水流动；***4)将这些模拟过程与观测结果进行比较；***5)预测未来多年冻土的退化。***研究地点位于加拿大魁北克省北部Umiujaq附近的不连续永久冻土带，那里富含冰的永久冻土丘已经在退化。在几个地点已经有了地温和融化沉降的长期监测系列数据。***本研究项目中使用的方法在很大程度上依赖于使用不同监测技术（自动热敏电阻电缆、水位记录仪、激光雷达调查以及可见光和红外摄影测量）、岩土和地球物理工具（永久冻土采样、电阻率和地震折射层析成像）以及对富含冰的永久冻土样本（解冻固结和水力导电性）的实验室测试所获得的实地观察结果。将进行热-水-机械过程的数值模拟，以模拟不同气候变化情景下的永久冻土退化。***本研究计划的预期结果是更好地理解在退化的永久冻土中发生的物理过程，并改进相变传热、融化固结、融水迁移和流动的数值模拟，以预测气候变化导致的永久冻土退化。从本研究项目中获得的知识，可以制定适应策略，以确保加拿大北部的可持续发展。

Among the geohazards associated with permafrost degradation which impact the sustainable development of Northern Canada, the vulnerability to thaw subsidence is widespread. The thaw consolidation of permafrost is closely related to water content, cryostructure, soil texture, rates of thawing and dissipation of pore water pressure. However, little is known on the fate of water from melting ground ice in degrading permafrost. How does the pore water dissipation control the thaw consolidation? Where the meltwater is flowing into the ground? Is the meltwater recharging the aquifers at depths or is it migrating at the ground surface and ultimately finding its way in lakes, rivers, and oceans? ***As a research hypothesis and a positive feedback, the thaw subsidence which depends on the dissipation of pore water pressure accelerates the rate of permafrost degradation. The warm boundary at the ground surface is moving downwards toward the degrading permafrost body at depths which increases the permafrost thawing. ***For testing this research hypothesis, the objectives are to: ***1) observe, describe, and monitor in the field the processes of permafrost degradation, ***2) measure the thaw consolidation properties of ice-rich permafrost from laboratory tests, ***3) simulate the heat transfer, thaw consolidation and flow of meltwater which are taking place in degrading permafrost, ***4) compare these simulated processes with the observations, and ***5) anticipate the permafrost degradation in the future. ***The study site is located in the discontinuous permafrost zone close to Umiujaq in northern Quebec, Canada, where ice-rich permafrost mounds are already degrading. Long-term monitoring series of ground temperature and thaw subsidence data are already available for several locations. ***The methodology used in this research program relies heavily on ground truth from careful field observations using different monitoring techniques (automated thermistor cables, water level loggers, LiDAR surveys and visible and infrared photogrammetry), geotechnical and geophysical tools (permafrost sampling, electrical resistivity and seismic refraction tomography), and lab tests on ice-rich permafrost samples (thaw consolidation and hydraulic conductivity). Numerical modelling of thermal-hydro-mechanical processes will be performed to simulate permafrost degradation following different scenarios of climate changes. ***The expected outcomes from this research program are a better understanding of the physical processes which are taking place in degrading permafrost and the improvement of numerical modelling of heat transfer with phase change, thaw consolidation, meltwater migration and flow to anticipate permafrost degradation due to climate changes. From the knowledge developed in this research program, adaptation strategies could be established to insure the sustainable development of Northern Canada.